Before I went to bed
last night I trolled through the eBay listings for an appropriate H-bridge; there were lots that were driven by logic-level inputs (3.3V, 5V) but only one design that I found that could use the 12V output of the AC12; that was the same one that the @lateral found above. I did find a lower price
. So typical of eBay - lots of listings but little choice.
The control logic inputs to the H-bridge should be very high impedance; barring an outright short I doubt they would threaten the AC12's MOSFETs. In any event I suspect the AC12 has over-current protection. Personally I think a fuse would be more likely to cause a failure then protect anything in this case (AC12>H-bridge).
I have never heard of a fuse between a driver and motor in an AP; it would be problematic as it would have to be large enough to handle the startup current (with a slow-blow fuse) but then might be too large for a continuous over-current. Again, it seems like more a problem than a solution.
The H-bridge referred to apparently does not have over-current protection, but instead offers a current monitor
output, in Volts. You could set up a comparator for a max current which could open the Enable input, which is probably a good idea if a bit more complexity.
@tanglewood: I doubt that the AC12 uses a variable voltage output, although that is just a guess. "Linear" is often part of the description for autopilot
drives, usually referring to an in/out ram, not the voltage control. Sufficiently accurate control can be achieved with PWM, there is no value in a slower response, and such control would be less efficient. Of course if that were the case it would call for a different solution.
@RaymondR: I have often wondered if any autopilots monitored the current draw of the drive, for protecting the output transistors, detecting a drive not connected condition, and to detect the end of travel (banging up against the stops) at an elevated current which could still be below an over-current condition. A simple over-current protection wouldn't be a problem for driving the H-bridge, but a resistor might be needed if the current is used for detection of drive presence or end of travel. Good thought - thanks.
It has been a couple of years since I last looked at using an H-bridge, so my memory is fuzzy and in any event this technology is not really in my wheelhouse so please feel free to amend/extend anything I have written.